Changes in Promoter and Inhibitor Substances during Dormancy Release in Apple Buds under Foliar-Applied Dormancy-Breaking Agents

AbstractThe effect of hydrogen cyanamide (Dormex) at different concentrations for reaching early break dormancy in buds of "Astrachan" apple (Malus sylvestris, Mill) trees and their effects on metabolic changes in the content of buds from promoter and inhibitor substances during their release from dormancy was investigated. The efficiency of early bud break was noticed in varying degrees with Dormex at different concentrations. All applied concentrations led to early bud break, short flowering duration, high percentages of bud break and fruit-set, high contents of total indoles, indole-3-acetic acid, gibberellic acid, total and conjugated phenols and low content of abscisic acid and free phenols. These results were positively reflected in the final yield. Accordingly, we recommend using Dormex at 3% for reaching the early break dormancy in buds of "Astrachan" apple trees under Egyptian winter conditions and maximizing the yield by regulating the hormonal and phenolic content in buds.